"Which is a very good point, although one school of thought has it that in such a culture human memory was far more acute at recording & recalling things than it is today. In Music Halls it's reported an audience could remember an entire song on a single hearing, likewise with lengthy lays in the Middle Ages. So how does this fit in with collective memory loss, or things changing by chance? Hmmmm..."

Because, SO'P, Buchan suggests that in a non-literate culture texts were not fixed and ballad singers had a sort of 'construction kit' in their heads from which they made a ballad anew each time that they sang it. The 'kit' contained such things as tunes, plot lines and standard phrases ('milk-white steed', 'lily-white hand' etc.). I recommend 'The Ballad and the Folk' - it's a bit of a revelation.